Vapor conserving tank



J. o. JACKSON 2,418,229

VAPOR CONSERVING TANK April l, 1947.

Filed Jan. 3l, 1942 23 Ill.k a n 1 .N ArroRNi-:Y

l 2 Sheets-Sheet l` April l', 1947.

J. o. JACKSON 2,418,229

VAPOR CONSERVING TANK s Filed Jan. 5l, 1942 2 Sheets-51166.?. 2, N /`1 l/,j

M ATTORNEY Patented Apr. ll, 1947 UNITED STATES PATENT OFFICE VAPOR. CONSERVING TANK James 0. Jackson, Grafton, Pa., assignor to Pittsburgh-Des Moines Company, Pittsburgh, Pa.,

a corporation of Pennsylvania l Application January31, 1942, Serial No. 429,050

6 Claims. l

This invention relates to tanks for the storagev having roofs expansible underincreases in vapor pressure. Many liquids, such as commercial gasoline, have a, vapor pressure when confined in a gastight storage tank. It is usually not economical to design such tanks with sufficient strength to resist such internal vapor pressure and to avoid the danger of failure of the tank it is common practice to place a vent usually in the tank roof so that the vapor may freely vent without causing increased pressure on the underneath side of the tank roof. This results ina substantial waste.

It has been found that if tank roofs are made flexible so that they may become expanded or inflated by the increasing volume of the liquid vapor the pressure on the tank roof may be kept within safe limits and with such construction it is only necessary to vent thetank when the inflatable roof has expanded or deflated to its safe limits. The economy of such a-tank is based upon the fact that the generation of vapor from the liquid requires an appreciable amount of time for it is necessary for the tank contents to slowly absorb heat from the suns raysor the outside atmosphere in order to permit such vaporization to continue. It Would, therefore, be most desirable to provide a storage space for the tank vapors which would approximately equal the volume of vapor at a safe pressure generated during the Warm daylight hours which vapors in the cooler night hours would condense to a liquid allowing the roof to deflate to its original position. This cycle would then be repeated from day to day with theoretically no loss of tank contents.

Inflatable roofs as heretofore devised have many objectionable features and frequently fail to function as intended. Roofs made of sheet metal which expand from a central position to an expanded position must depend for their operation on the sheet metal buckling as its collapses, such buckling frequently causing sharp bends, kinks, and fatigue failure of the metal. Other types work on the principle of a reversal of shape. This type has the serious objection that due to the inherent resistance of a portion of a conical or spherical surface considerable pressure maybe built up before the roof reverses and when reversal does occur under these conditions the shock or impact over a relatively large area may cause failure of the surfaces through rupture and when this occurs fire frequently -results from sparks struck by the sliding surfaces.

It is the primary object of my invention to provide an improved inflatable or vapor conserving roof of novel construction which is substantially free of the above objections.

Another object of my invention is to provide an inflatable roof of the reversing type in which the reversing action ls controlled so that it will proceed smoothly as the roof inilates andV deilates.

Another object of my invention is to provide a construction in which the bending of the sheet metal at the critical point is spread 'out over` a relatively large area and, therefore, reduced in intensity.

Still another objectof my invention is to provide a vapor conserving roof which will reduce the vapor space to as small a volume as possible, with sufficient flexibility and control to reduce the venting losses therefrom to an economical minimum. A still further object of my invention is to provide a roof which can be very economically built from steel sheets which need not be pressed or formed for if, as contemplated by my invention, the roof is laid out and built upon the structural supports devised by me to support it in :its deflated position it will, from the inherent geometry, t exactly in the expanded position.

To these ends I provide a flexible :roof which in the down or deflated position rests on circular rafters set at different elevations tc produce a predetermined double curvature, designed to permit the roof to flex smoothly from the deflated to the inflated position. The theoretical area of the roof plating being equal i the deflated and in# l flated position there is no tendency for buckling in vthese positions. In passing through the intermediate positions the roof sheets are subjected to a nominal radial compression which is: kept within conservative limits. Due to the fact that the curvature of the exterior portion of the roof is reversed from that of the interior portion, when the roof is in its deflated position, there is set up in the metal a bending stress which causes the roof to expand smoothly from the outside towards the center as the vapor volume increases vand to collapse smoothly from the center to the outside as the vapor volume decreases. This roof shape avoids dificulties which have been experienced with roofs of conical or truncated conical shape. This feature is important because unless the roof action is smooth excessive pressure is apt to be built up which may cause the roof to expand or collapse vvery suddenly, causing shock failure with a possibility of fire or explosion.

Another advantage inherent in my design is that the roof plates where they connect to the my invention or claims thereto, certain preferred embodiments of my invention: A

Fig. 1 is a vertical sectional view; showing one form of my tank;

Fig. 2 is a half-plan view with a portion of the will flex to position IIl When `the roof has' reached its full expansion it will be in position III. In that position the initial bending stress will be almost entirely relieved except at the outer periphery.

It is, therefore, apparent that due to my novel construction which takes advantage of the elastic property of steel sheets the radius of the initial curve of the roof sheets above rafterglg will gradually increase and extend inwardly'as thetank roof inates until, when it reaches its full inroof sheets removed to show the arrangement of the supporting framing; I

Fig. 3 is an enlarged sectional view of the upper corner showing more clearly how the roof flexes as it expands, and

Fig. 4 shows another form ofthe 4device which provides for larger capacities. y

Referring to the drawings, there is shown"A in Fig. `1 a relativelythin sheet metal roof 4 formed of a plurality of sheets attached together at their edges as by welding. The roof is attached about y its periphery to the upper portion of the tank,

preferably to the top angle member 5 which in turn is secured to the upper periphery of the cylindrical tank shell 5.

The flexible sheet roof 4 is originally built. on the circular rafters 1, 8, 9, I0, II and I2 which in .turn are supported bygirders I3 and I4. In order to give the desired curvature to the roof when in deflated condition,v while maintaining standard size of the rafters, the rafters 1, 8 and 9 are preferably provided with intermediate supports l', 8' and 9', respectively, connecting them to said girders. By this construction the roof is divided into acentral circular portion convexed downwardly and anouter annular portion convexed upwardly. Each girder I3 is conveniently supported at its outer end by attachmentto tank shell 6, as by welding, and at its inner end upon beam I5. Each girder I4 is preferably supported at its inner end on -a platform I6' mounted on the top of a column I6 and at its outer end on beam I5 which in turn is supported by columns I1.

A valve I8 attached to a housing I9 surrounding a central opening 20 in the roof sheets is operatedby chain 2I which when the roof has expanded to a predetermined safe point opens to relieve any further increase 'of internal pressure which might cause failure.

Water accumulating inthe central 'portion of the roof when it is in a deated position is conducted down pipe 22 into the tank. Said pipe at itslupper end extends through and is secured to said roof structure as by welding and at its lower end is slidably engaged by the support 23 at tached to the column I6.

In Fig. 3 the roof is shown in its initial or deflated position I; The roof sheet 4 is sprung tions-and that changes in construction and ardated position III the vcenter portion will have risen to a `point where no sudden reversal with damaging effects will take place.

Another form of myv device is shown in Fig. 4. In this form the roof sheets 4' are flexed over the cylindrical tank shell 6 and extend a considerablev distanceon the outside of the tank. Roof sheets'4' are, however, not connected to tank shell 5 directly but are connected to annular sheets 24 which in turn are connected to tank shell 6 through reinforcing top angle member 5 to which it is attached as by welding. It is apparent that this construction increases considerably the vapor capacity of the roof not only `because of its larger diameter but because of .the

addedi capacity obtainedby the flexibility of the annularly arranged sheets 24.

While I have shown and described certain preferred embodiments of my invention it is to be understood that it is capable of many modicarangement may be made therein without departing from the spirit and scope of my invention. I therefore desire to covr in the claims all novelty in my invention over the prior art.

What I claim as new and desire to secure by Letters Patent is: i

1. In combination, a tank for volatile liquids and the like, an expansible sheet metal roof attached thereto about its periphery, and annular means for supporting said expansible roof in its y lowermost or unexpanded position while maintaining an outer circular zone of said roof for an appreciable distance inside its outer periphery at a height to prevent appreciable angular change between said roof and tank at their line of attachable manner so that the roof sheet 4 Vhas an initial bending stress extending from angle member 5 inwardly. When the temperature of the tank contents increases gas pressure is exerted on the entire interior of the tank and on the underneath side of th roof sheets 4; lWhen the internal pressure approaches the `weight of the roof sheets per unit of area the roof sheets ment to each other, said supporting means being adjacent to and spaced radially inwardly from the periphery of the roof intermediate the `axis 'of the tank and its periphery and extending above said periphery to permit the central portion of the roof to be dished to present a convex-surface toward the interior of the tank when the roof is deflated.

2. The combination defined by claim 1 in which the-roof extends beyond the upper periphery of said tank and is provided with an inwardly exe tending ilexible portion attached at its inner edge to said tank. y y

3. An inflatable elastic sheet metal storage tank roof having its peripheral portion rigidly attached to said tank; a support therefor disposed around fthe axis of the tank between said axis and the periphery of the tank and spaced therefrom, and extending above the plane of the attachment of said roof to the periphery f the tank a distance suiiicient to cause the portions of said roof on radially opposite sides of said supporting means to have radii of surface curvatures in -reverse directions when lthe tank is deiiated, the radius of curvature of the peripheral portion of said roof at all times extending downwardly, said support contacting the underside of said approximately 4free of 'i rafter 1 relieving the initial bending stress.-

peripheral portion of the roof when denated; the mid-portion of said roof in deilated position extending below the peripheral portion.

4. A tank adapted to contain a volatile liquid; an expansible sheet metal roof therefor rigidly attached to said tank at its upper periphery; a

support for said roof in it-s lowermost positionI when the 'tank is deilarted comprising aseries of vertically supported radially spaced coaxially arranged circular girder-like rings the outermost of which has its supporting edge above the upper periphery of said tank and in spaced relation thereto and the inner rings of which have itheir supporting edges lower than the supporting edge of said outermost iing,'progressively toward the.

tank axis.

5. A tank, adapted to contain a volatile liquid; an expansible sheet metal roof therefor having .its peripheral edge rigidly attached io the upper periphery of the tank; a support for said yr'oof when in its lowermost position due to deflation of the tank, comprising a coaxially arranged outer supporting portion having its supporting edge at suiicient height above the upper periphery of the tank and in spaced relation thereto, to contact the outer peripheral portion of the roof inwardly of its periphery to limit the ilexure of the portion of said roof adjacent its attachment to the tank during the operation of said roof to prevent plastic deformation, and a coaxially arranged supporting portion spaced inwardly from the outer supporting portion and having its supporting edge lower than the peripheral edge of the roof, the

' outer peripheral portion of the roof which is contacted by the first mentioned supporting portion having a radius of curvature downwardly at all times.

6. The method of constructing an iniiatable sheet metal roof for a. storage tank comprising to each other and to the sheets which are to form l the outer portion of the roof, leaving the sheets of the latter unjoined to each other; ilexing the free ends of the outside roof sheets over said outermost ring downwardly into contact with the top of the tank, and rigidly joining said ends thereto and the adjacentl edges of said outer sheets to each other, whereby said outer portion of the roof is prestressed to a curvature having a downwardly extending radius causing it to expand smoothly and without buckling.

JAMES O. JACKSON.

REFERENCES CITED The following references are of record in the ille of this patent: l

UNITED STATES PATENT Number Name Date 1,846,506 Wiggins Feb. 23, 1932 1,809,013 Boadman June 9, 1931 1,645,313 Wiggins Oct. 11, 1927 1,911,988 Chevalier May 30, 1933 2,114,513 Wilkin Apr. 19, 1938 1,731,283 Wiggins Oct. 15, 1929 1,846,294 Wiggins Feb. 23, 1932 i 1,726,281 Wilson et al. Aug. 27, 1929 Wiggins July 11, "1933 

